The present invention relates to a thermoplastic elastomer composition whose volume resistivity can be controlled within a wide range of from 104 to 1013 (xcexa9xc2x7cm) and a method for controlling the volume resistivity of a composition so that it can have a desired conductivity.
Recently, in a product to which a composition having a conductivity is applied, such as an OA appliance, a semiconductive rubber composition and a thermoplastic elastomer composition having a resistivity in a region on the order of 105 to 109 (xcexa9xc2x7cm) (in a semiconductive region) has been increasingly demanded.
However, conventionally, semiconductive rubber compositions have been controlled of the resistivity of the composition by imparting conductivity by addition of conductivity imparting agents having conductivity, such as carbon black. For this reason, a decreased amount of conductivity imparting agent is added in order to adjust the resistivity to a region on the order of 105 to 109 (xcexa9xc2x7cm). However, it is extremely difficult to uniformly disperse the conductivity imparting agent in the composition in low concentrations and there arises the problem that the resultant composition has a resistivity that fluctuates to a greater extent. To solve this problem, it is necessary to improve the dispersibility of conductivity imparting agents and many proposals have been made to allow conductivity and dispersibility to coexist but their improvement has been difficult and no semiconductive composition that can be put to practical use has been obtained yet.
Japanese Patent Application Laid-open No. Hei 3-89357 proposes a semiconductive belt for OA appliance made of polycarbonate containing a conductive carbon. However, it is very difficult to control the resistivity of the polymer composition in a semiconductive region and it is almost impossible to obtain a desired resistivity by addition of a conductive carbon to ordinary polymers.
As described in, e.g., Sumita, et al., Kobunshi Kakou (Polymer Processing), Vol. 43, No. 4 (1994), according as carbon is added increasingly in a polymer, the conductivity of the mixture remains low (resistivity is high) while the amount of carbon added is small and after a certain threshold the carbon forms a conductor circuit and the conductivity increases abruptly (resistivity decreases) so that medium resistivity cannot be obtained.
In the case where a foam such as urethane foam is utilized as the semiconductive composition, the distribution of the conductive imparting agent in the foam depends of the condition of the foam so that it is difficult to control such that the distribution becomes uniform and it is also difficult to obtain a semiconductive composition having a non-fluctuating resistivity using a foam.
One object of the present invention is to provide a thermoplastic elastomer composition having a desired volume resistivity. Preferably, the present invention is to provide a thermoplastic elastomer having a conductivity (volume resistivity) from a conductive region (104 ((xcexa9xc2x7cm) or less) to an insulating region (1013 (xcexa9xc2x7cm) or more), more preferably from a conductive region (104 (xcexa9xc2x7cm) or less) to an insulating region (1010 (xcexa9xc2x7cm) or more), or furthermore in a semiconductive region (105 to 109 (xcexa9xc2x7cm)) and a method of controlling the volume resistivity of a composition so as to have a desired conductivity.
That is, the present invention provides a thermoplastic elastomer composition comprising a thermoplastic resin as a matrix phase and a rubber particle at least a part of which is crosslinked as a domain phase, wherein the rubber particle is a rubber particle at least a portion of which has a conductivity to give the composition a controlled volume resistivity.
The controlled volume resistivity of the thermoplastic elastomer composition is preferably 104 to 1013 (xcexa9xc2x7cm) and more preferably 104 to 1010 (xcexa9xc2x7cm)
Preferably, the rubber particle contains a conductivity imparting agent selected from metal powder having a volume resistivity of 10xe2x88x926 to 10xe2x88x921 (xcexa9xc2x7cm) and/or conductive carbon black.
The controlled volume resistivity of the thermoplastic elastomer composition is preferably 105 to 109 (xcexa9xc2x7cm).
Preferably, the rubber particle is of a two layer structure which comprises a core and an outer layer and at least the outer layer contains the conductivity imparting agent.
The present invention provides a method of controlling a volume resistivity of the composition, comprising controlling a volume resistivity of the composition comprising a thermoplastic resin as a matrix phase and a rubber particle at least a part of which is crosslinked and which contains a conductivity imparting agent as a domain phase, by controlling of volume fraction of the rubber particle having a conductivity, size of rubber particle containing the conductivity imparting agent, dispersibility of rubber particle containing the conductivity imparting agent, or structure of rubber particle.